The present invention relates to a method for applying a protective coating to the components of a printed circuit board, said coating being comprised of a polymerizable material such as a resin.
Protection of components of printed circuit boards used in a harsh environment (temperature, moisture, impacts, vibrations, etc.) by applying to them a coating comprised of a polymer resin is known. Such an operation is often called "varnishing" or "tropicalization" of boards.
In general, a protective coating is made of a single layer of resin applied by sprinkling, or by spraying, or by dipping the board in a liquid resin bath.
However, the protection provided by this resin layer often proves to be inadequate. The complexity of printed circuit boards, due to the presence of active and/or passive components of highly variable size and fragility such as connectors, the various housings of electronic or integrated-circuit components, etc. requires protective coatings of different types depending on the type of component in question. To accomplish this, different molds and different types of resins have to be made for selectively applying an appropriate coating to each type of board component. Specifically, connectors require a coating based on a viscous resin for impact strength in particular, while components of SMD (surface mounted device) housings require protection against moisture for example by means of a highly fluid resin for small housings or a semi-viscous resin for larger housings. As a result, protection of the various components on a single printed circuit board requires production of a resin-holding mold for each component type so that the resin is applied selectively without flowing beyond the component to be protected.
This being the case, protection of the components on a printed circuit board requires prior fabrication of several molds and a coating operation for each mold used. Implementation is lengthy and complex, resulting in very high manufacturing costs.